Chemosphere - Global Change Science最新文献

We report the development and application of analytical techniques for atmospheric N₂O based on Fourier transform infrared (FTIR) spectroscopy. Using mobile low resolution (1 cm⁻¹) FTIR spectroscopy in the field, the technique delivers mixing ratio measurements of precision ±0.3 ppbv (0.3 nmol mol⁻¹) N₂O and in situ soil–atmosphere flux chamber measurements of fluxes less than 1 ngN m⁻² s⁻¹ (0.04 nmol N₂O m⁻² s⁻¹) with a time resolution of 30 min. The method offers the additional advantages of being simultaneously able to measure CO₂, CH₄ and CO mixing ratios in air to high precision (±0.15 μmol mol⁻¹, ±1 nmol mol⁻¹, ±0.3 nmol mol⁻¹, respectively). By a similar analysis procedure, but with laboratory-based high resolution (0.012 cm⁻¹) FTIR spectroscopy, the N₂O isotope ratios δ¹⁵N, δ¹⁸O and δ¹⁷O are determined simultaneously for a single sample, with current precision of $\text{±1.0‰,}\text{±2.5‰}$ and $\text{±4.4‰}$, respectively. FTIR also resolves the individual contributions of the ¹⁵N¹⁴N¹⁶O and ¹⁴N¹⁵N¹⁶O to overall δ¹⁵N. The resolution of these two isotopomers is not possible using conventional isotope ratio mass spectrometry (IRMS). We present laboratory results demonstrating precision, and N-positionally resolved δ¹⁵N and δ¹⁸O measurements of UV-photolysed N₂O in which a distinct asymmetric ¹⁵N positional effect is observed.

Tropical peatlands could be a potential source of nitrous oxide (N₂O) which has a significant impact on global warming. To reduce N₂O emission and develop best management practices for peatlands, the formation and emission rates of N₂O as affected by land-use management (i.e., changing peatland into agricultural land) and the factors affecting the process must be understood. Therefore, one field and three laboratory incubation experiments were carried out during 1998–99 using peatland soils from 12 sites in South Kalimantan (Indonesia) and one site in Sarawak (Malaysia) to quantify the N₂O emission and the factors affecting it. The results from the field experiment showed that land-use managements, changing water table and locations had a significant impact on N₂O emission. Changing peatland into cultivated lands (cultivated upland and paddy field) enhanced the N₂O emission. For example, cultivated upland Cassava crop resulted in the highest amounts of N₂O emission (1.04 mg N m⁻² h⁻¹) compared to other treatments. The N₂O emission during 1998 was higher than those during 1999 because of the changing water table and dry season in 1998. The laboratory experiments showed that the N₂O emission was also strongly influenced by land-use management, soil moisture contents, addition of ammonium fertilizer or rice straw and soil depths. For example, the flooded conditions stimulated the N₂O emission compared to that at 60% moisture contents. Similarly, the addition of ammonium fertilizer suppressed the N₂O emission compared to control treatments because of the high ammonium contents that inhibit nitrification. Nevertheless, incorporation of rice straw to soil samples from 20 to 40 cm soil depth stimulated N₂O emission.

Estimates made by the Intergovernmental Panel on Climate Change (IPCC) and the Australian National Greenhouse Gas Inventory Committee (NGGIC) suggest that grazed pastures are substantial anthropogenic sources of nitrous oxide (N₂O), contributing 28% of all anthropogenic N₂O emissions globally and >43% for Australia. These estimates are based almost wholly on extrapolations of enclosure experiments to the field scale and uncertainty levels are high. Verification with direct field measurements is needed. This paper reports micrometeorological studies of N₂O emissions from Australian grazed pastures made at the same location on a variety of space scales. They included a mass-balance study employing a small test plot approximately 0.05 ha in area in which 14 sheep were grazed, tower-based flux measurements representing areas between 25 ha and 5 km² and convective boundary-layer budgets representing regions of order 100 km². The mass-balance study, which was considered to be the most reliable micrometeorological approach, gave an average emission over 8 days of 1.87 g N₂O–N head⁻¹ d⁻¹ corresponding to 11.5% of the nitrogen (N) voided by the animals in urine and dung. However, the data set included two days after rain on which emissions were an order of magnitude larger than on the other days in the study. For the latter, the emission of N₂O accounted for 3.9% of the N excreted. Although uncertainty levels remain high due to large temporal and spatial variability, the micrometeorological measurements suggested that N₂O emissions might be considerably larger than those predicted by NGGIC algorithms which use emission factors of 0.4% for urine and 1.25% for dung, but appear to be predicted more closely by IPCC algorithms which use 2% for both. The study has indicated ways to improve the precision of relevant micrometeorological approaches.

N₂O emissions from agricultural, forest and grassland ecosystems in China were in situ measured by closed chamber method, and estimation of total annual N₂O emissions from these ecosystems and a technique mitigating N₂O emission from agricultural soil were reported. The results showed: (1) the annual emissions of N₂O from rice, maize, soybean and wheat field, temperate forest and temperate grassland in China were 1.08–2.99, 0.47–4.51, 1.98, 1.02–2.93, 0.28–1.28 and 0.27–0.61 kg $\text{N}{}_2\text{O}\text{–}\text{N}\text{ha}{}^{\mathrm{-1}}$, respectively. The total annual N₂O emissions from agricultural, forest and temperate grassland ecosystems in China were estimated as 152.49, 94.10 and 112.13 Gg N, respectively. Industrially co-crystallized ammonium bicarbonate (AB) with dicyandiamide, substituting for ammonium bicarbonate in China, decreased N₂O emission significantly from a meadow brown soil in laboratory (80.2% at soil moisture 12% and 40.0% at soil moisture 22%, respectively) and upland field condition (74.0%).

Today our understanding of the sources and sinks of nitrous oxide (N₂O) may be at a turning point. Currently, it is believed that there are no atmospheric photochemical sources of N₂O and that microbial activity at the earth's surface (soil, lake, ocean, etc.) is the major source of atmospheric N₂O. Anthropogenic activities are thought to release N₂O into the atmosphere, but their magnitude is uncertain and probably minor. Here we present estimates of atmospheric production of N₂O from excited ozone (O₃) based on comprehensive laboratory experiments. These experiments covered a large range of pressures from 1 to 1000 torr to distinguish between the various possibilities on the basis of their pressure dependencies, and used two reaction vessels of widely varying surface-to-volume ratios to distinguish between surface and gas phase reactions. Never before in the history of the experimental studies of N₂O under atmospherically significant conditions has such a comprehensive coverage of the parameter space been attempted. From this data, the atmospheric production is substantial, being around 40% of its “classical” source strength. In order to put the atmospheric production in proper perspective, we also present those considerations that led us to look into the atmospheric sources. If we accept the IPCC’s 1990 position on the N₂O source-sink inventory, then the atmospheric production of N₂O bridges the source deficits. On the other hand, if the later IPCC positions of a nearly balanced inventory is accepted, then the new source means that either the post-1990 IPCC methodology for establishing national inventories of greenhouse gas emissions overestimates N₂O emissions or there exists some hitherto unrecognized sinks of N₂O.

Context Abstract: Nitrous oxide (NO₂) is a potent greenhouse gas whose atmospheric budget is poorly constrained. One known atmospheric source is the formation of N₂O on three-way motor vehicle catalytic converters followed by emission with the exhaust. Previous estimates of the magnitude of this N₂O source have varied widely. Two methods employing tunable infrared lasers to measure N₂O/CO₂ ratios from a large number of on-road motor vehicles have been developed. Both methods add support to lower estimates of N₂O emissions from the US motor vehicle fleet, although significant uncertainty remains.

Main Abstract: Two tunable infrared laser differential absorption spectroscopy (TILDAS) techniques have been used to measure the N₂O emission levels of on-road motor vehicle exhausts. Cross road, open path laser measurements were used to assess N₂O emissions from 1361 California catalyst equipped vehicles in November, 1996 yielding an emission ratio of (8.8±2.8)×10⁻⁵ N₂O/CO₂. A van mounted TILDAS sampling system making on-road N₂O measurements in mixed traffic in June, 1998 in Manchester, New Hampshire yielded a mean N₂O/CO₂ ratio of (12.8±0.3)×10⁻⁵, based on correlated N₂O and CO₂ concentration peaks attributed to motor vehicle exhaust plumes. The correlation of N₂O emissions with vehicle type, model year and NO emissions are presented for the California data set. It is found that the N₂O emission distribution is highly skewed, with more than 50% of the emissions being contributed by 10% of the vehicles. Comparison of our results with those from four European tunnel studies reveals a wide range of derived N₂O emission indices, with the most recent studies (including this study) finding lower values.

Nitrous oxide (N₂O) plays an important role in ozone chemistry as well as in greenhouse warming. It is the source of NO_x radicals in the stratosphere which are the dominant catalysts for ozone depletion. Recently, doubts have been raised on the global N₂O budget. One approach to solve this problem has been the consideration of new mechanisms for atmospheric production and destruction of N₂O. In parallel, N₂O sinks have been constrained from observed tracer correlations in the lower stratosphere based on aircraft measurements, which are limited up to an altitude of only 20 km. We use vertical distributions of N₂O and other trace gases measured simultaneously from Hyderabad, India (17.5°N, 78.6°E) in 1987, 1990, 1994 and 1998 using balloon-borne cryogenic air samplers covering the altitude range of about 8–37 km to study these issues together with 2-D model simulations. The slopes of N₂O correlations with CH₄, CFC-12 and CFC-11 compare well with the model derived slopes, with exceptions in cases where dynamical perturbations are strong. Average N₂O lifetimes of 85±43 and 111±38 years have been estimated using the observed slopes and two sets of reference lifetimes for the correlated tracers. This average lifetime compares well within the spread, with the lifetime estimated from the sink of N₂O in the model, suggesting that the present estimate of the N₂O photochemical sink incorporated in the model is adequate.

Adipic acid (AA) is the main intermediate in nylon 6, 6 that is manufactured by polymerization condensation of AH salt (hexamethylenediammonium adipate). Adipic acid is also an intermediate in the production of polyester-polyol, a material used in polyurethane.

Annual production capacity of AA for 1998 was estimated to be 2.3 million metric tons and about 80% of that AA is used to manufacture nylon 6, 6. Almost all AA is produced by nitric acid oxidation of KA oil, a mixture of cyclohexanone and cyclohexanol.

The reaction of nitric acid oxidation unavoidably generates nitrous oxide. The N₂O emission coefficient for Japan's AA plant is approximately 0.25 kg-N₂O/kg-AA. If the N₂O output from all adipic acid plants is calculated using the N₂O emission coefficient described above and the world's AA production capacity then we obtain a figure of 576,250 metric tons per year, but if we calculate only that which will be clearly reduced by 1999–2000, a reduction of ca. 80% has already been achieved. This is because the N₂O abatement equipment of the major AA manufacturers is scheduled to have completed startup by 1999–2000.

The main technologies used to reduce nitrous oxide in the adipic acid industry are catalytic decomposition and thermal destruction. These methods convert nitrous oxide into nitrogen and oxygen. Catalytic decomposition operates at about 500°C and thermal destruction operates at and over 1000°C. Using these reduction technologies allows the adipic acid manufacturers to reduce N₂O emissions by 90% or more.

Three nitrogen chemical fertilizers were applied to soil – controlled-release urea (CU), a mixture of ammonium sulfate and urea with nitrification inhibitor (AM), and a mixture of ammonium sulfate and urea with no nitrification inhibitor (UA). N₂O and NO fluxes from an Andosol soil in Japan were measured six times a day for three months with an automated flux monitoring system in lysimeters. The total amount of nitrogen applied was 20 g N m⁻². The total N₂O emissions from CU, AM and UA were 1.90, 12.7, and 16.4 mg N m⁻², respectively. The total NO emissions from CU, AM and UA were 231, 152, and 238 mg N m⁻², respectively. The total NO emission was 12–15 times higher than the total N₂O emission. High peaks in N₂O and NO emissions from UA occurred for one month after the basal fertilizer application. The N₂O emissions from CU and AM during the peak period were 50% of those from UA, and the NO emissions were less than 50% of those from UA. After the peak period, the N₂O and NO emissions from CU were the highest for two months. A negative correlation was found between the flux ratio of NO–N to N₂O–N and the water-filled pore space. A diel pattern with increased N₂O and NO fluxes during the day and with decreased fluxes during the night was observed.

We have studied the effect of soil compaction on N₂O fluxes in relation to gas diffusion and N fertilization in the field, and N₂O release rates in laboratory incubated soil samples. The fertilization and soil compaction field experiment was established in 1985, and the gas fluxes were measured in the period from 1992 to 1994. N₂O emission was higher in compacted than in uncompacted soil. This compaction effect was four times higher in the NPK-fertilized treatment compared to the unfertilized one. Soil compaction decreased gas diffusivity and this may have contributed for increased N₂O emission. This increased N₂O emission due to soil compaction in the field became non-significant after the compacted soil was sieved (2-mm mesh) and N₂O emission rates were measured in laboratory incubations. The sieving presumably removed diffusion barriers and increased the oxygen supply compared with that under the soil compaction in field. This reversibility of field compaction effects indicates that the soil compaction does not permanently increase the biological potential for N₂O production in the soil.